Polyolefins are plastic materials useful for making a wide variety of valued products due to their combination of stiffness, ductility, barrier properties, temperature resistance, optical properties, availability, and low cost. One of the most valued products is plastic films. In particular, polyethylene (PE) is the one of the largest volume polymers consumed in the world. It is a versatile polymer that offers high performance relative to other polymers and alternative materials such as glass, metal, or paper. Plastic films such as PE films are mostly used in packaging applications but they also find utility in the agricultural, medical, and engineering fields.
PE films are manufactured in a variety of grades that are usually differentiated by the polymer density such that PE films can be designated for example, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE), wherein each density range has a unique combination of properties making it suitable for a particular application.
Heat sealing is the major technique used for forming and closing flexible packages. Heat is used to rapidly activate a sealant layer comprised of a heat sealable material, usually a polymeric material. The temperature required to activate the heat sealable material and form a durable seal is termed the seal initiation temperature (SIT) and the ability of the seal to resist opening immediately after being formed is termed hot tack. The temperature range over which a durable seal can be formed and maintained is termed the hot tack window while the strength of the seal formed is termed the heat seal strength.
One factor in the use of these polymers as sealants is the thermal properties of the materials. Thus an ongoing need exists for polymers (e.g., PE) having improved thermal properties.